[land-bot] Add a sanity rebase after running smoke tests

Summary:
This ensures that any non-colliding changes pushed upstream within the few minute
window that smoke tests were running will not break the git push. While we do make
the assumption that tests still pass after this, breaking changes from automated
diffs should be exceedingly rare. For human-authored changes, we have a land queue to
help mitigate this.

This is copied from automated-commits.sh to bring this script up to
par with the sanity checking we already do there. The next step is to cleanup
automated-commits.sh so that it calls land-patch.sh directly.

Depends on D7467 and D7911

Test Plan:

cmake -GNinja -DENABLE_SOURCE_CONTROL_TOOLS_TESTS=ON ..
ninja check-source-control-tools

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7468